


inter eos

by armethaumaturgy



Category: Undertale (Video Game)
Genre: Begging, Ecto-Genitalia (Undertale), Explicit Sexual Content, Hand Jobs, Horror (Horrortale)/Nightmare (Dreamtale)/Dust (Dusttale), M/M, Overstimulation, Praise Kink, Threesome - M/M/M, Vaginal Fingering, Vaginal Sex, is this dust's first time? no. but is this his first time with the two of them? yeah
Language: English
Status: Completed
Published: 2021-01-24
Updated: 2021-01-24
Packaged: 2021-03-16 11:33:41
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,064
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28955760
Author URL: https://archiveofourown.org/users/armethaumaturgy/pseuds/armethaumaturgy
Summary: “You can join at any time if you want,” Nightmare speaks up. Dust lifts his gaze to find Nightmare’s trained on himself. His eyelight is as blown as Horror’s, almost feral and hungry. Horror’s sockets flutter as he blinks, nodding absently.“I’d… rather not,” Dust mutters, shifting in his seat. He can’t deny being aroused, especially while seeing his lovers enjoying themselves so much, but anxiety stirs in the pit of his stomach.
Relationships: Sans/Sans (Undertale)
Comments: 9
Kudos: 138





	inter eos

**Author's Note:**

  * For [Hella_D_Altar](https://archiveofourown.org/users/Hella_D_Altar/gifts).



Dust watches, enraptured, as Horror jerks, body going rigid in Nightmare’s hold. Nightmare’s hand, the one not currently burying fingers in the bigger skeleton, holds him close so he doesn’t fall over, tentacles wrapped around his femurs.

Even despite being on his knees, Horror’s legs tremble and he does look ready to fall over if Nightmare stopped holding him. Dust can’t keep his eyes off of Horror’s sweat-slicked bones, the joints flaring with rust-tinted magic with each ripple of pleasure that courses through him.

“You can join at any time if you want,” Nightmare speaks up. Dust lifts his gaze to find Nightmare’s trained on himself. His eyelight is as blown as Horror’s, almost feral and hungry. Horror’s sockets flutter as he blinks, nodding absently.

“I’d… rather not,” Dust mutters, shifting in his seat. He can’t deny being aroused, especially while seeing his lovers enjoying themselves so much, but anxiety stirs in the pit of his stomach. 

_‘Smart_ ,’ Papyrus whispers, close enough for his scarf to brush against Dust’s arm. He wretches it away like he’d been scorched. _‘It was probably just a courteous question at best. Like they’d want you between them.’_

Both of them look over to his left, where he’s glaring, straight at the specter as if they could see it, and Horror’s teeth split into a wide grin, all sharp edges and liquid danger, but his eyes crinkle at the corners cutely. His smile is sweet.

His hand, shaking profusely, reaches out and snatches the air. Papyrus’ face, morphed into indignation and anger, dissolves like smoke in the air.

Dust stares at that hand, shaking himself, but he doesn’t shy away when it comes to brush his cheekbone, softer than he’d expected.

“Are we free of _onlookers_ now?” Nightmare asks, and the teasing tone in his voice is offset by the serious stare he pins Dust in place with.

Dust can only nod.

Horror pushes at Nightmare’s chest, pushing him away. Nightmare’s fingers squelch as they pull out of Horror’s entrance, slick with the red fluids. Horror drops onto all fours, crawling over the king sized bed to pull at Dust’s arm, yanking him out of his seat on the chair.

“How about we... take care of everything instead?” he proposes, rising back up and maneuvering Dust between the two of them.

Dust opens his mouth to argue, maybe try to convince them again that this isn’t a good idea, Papyrus’ words replaying in his mind like a broken gramophone, but Nightmare starts sprinkling kisses along his vertebrae, pulling away the fabric of his hoodie and leaving him too exposed. 

Horror’s hands roam his body, following up the lines of his ribs, skirting his spine, just firm enough not to tickle. He itches to yank away, but Horror presses further into his back, flush and nestling his chin on top of his shoulder.

“Let’s get you out of these clothes, hmm?” Horror whispers, sliding his hand underneath the hem, fingers splaying over Dust’s sternum.

Dust’s SOUL flutters and he lets the two maneuver him as they want, raising his arms so they can slide the shirt off of him after slipping his hoodie off. He ends up leaning backwards, pulled by Horror as he sits, propped up by the pillows. Hands are everywhere and he can feel a couple of Nightmare’s tentacles, but he loses track of them quicker than he ever expected to.

Nightmare’s fingers slip beneath the hem of his shorts and shimmy them off, leaning over to press kisses along as he goes. Dust frowns as he gets to his foot, kissing the ankle and looking up with half-lidded eyes and a half-smirk.

“How are we doing?” he asks.

Dust blinks. “I— what?”

Nightmare snorts, chucking the shorts away somewhere to the floor where they create a pile with the other clothes. “We want you here,” he says, “That’s what I’m getting at.”

“Oh…”

Nightmare and Horror exchange a laugh over his quiet amazement, and go right back to what they had been doing previously; Horror’s hands dance across his ribcage, claws dragging across the length of the ribs. Whenever he runs over one of the floating ones, Dust’s body jerks a little, and it doesn’t escape the other’s notice. He deliberately runs over those the most. Sharp teeth hover right over his ear, hot breath fanning over the side of his head.

That by itself would’ve been more than enough to overwhelm him, but Nightmare starts going back up his legs, kissing and suckling on the bones. When he gets to his femur and drags his tongue over the length of it, Dust jolts in their holds.

“Ah—” he moans, raising a hand to grip at Nightmare’s shoulder, fingers trembling just a little bit.

“Oh… seems you found one of his spots,” Horror pokes, fingers pinching Dust’s lowermost rib. His hips rut against Dust’s back and the breath in his ear gets heavier with an exhaled moan.

“I wanna find a lot more than just one,” Nightmare shoots back, going back and splaying his hands across Dust’s where he’d just licked and pushing his leg outwards so he can nestle between them.

One of those sinful hands rubs across his pubic symphysis, and the magic that had been gathering in his crotch snaps into place with an audible crackle as soon as he pulls away.

Dust looks down, SOUL skipping when Nightmare’s breath fans over his cock. He didn’t even notice he had gotten so close, and now he’s hyper aware of it, watching the way Nightmare grins up at him like he’d been enchanted.

“Cute,” Nightmare mutters, running a finger over the lilac cock, all the way from the base to the tip, collecting a drop of his precum from the slit. He shamelessly licks it off, looking back up at the two watching him intently. “Almost like Horror’s. A little sweeter, maybe.”

“...jerk,” Horror huffs, pretending to pout as he goes to mark the small patch of unblemished bone on Dust’s shoulder.

Nightmare sticks out his tongue at him, childishly, and then drags it over the hard cock right after. Dust cries out, curling up and bucking. Both of them hold him still, Horror pulling him back against himself and Nightmare pushing down his hips, and he sobs, shaking as Nightmare’s tongue drags over his sensitive skin.

“Do you like that?” Horror asks, straight into his ear, and Dust, unable to answer vocally, can only nod vigorously. Horror’s grin is tangible as he smothers it in Dust’s neck. “You’re... so cute. How long’s… it been?” A jerky shrug for an answer. “You should join us more often, you’re… so pretty like this,” Horror keeps chattering, “I love your reactions, you… practically jump whenever I touch you. And we haven’t even started.”

A sound, somewhere between a whine and a guttural groan, rips out of Dust’s throat, and even Nightmare looks up at that, wiping his mouth with the back of his hand.

“Huh.”

Horror’s expression is a wicked smile, eye sparkling with mischief. “Ohh…” he teases, “You like it when… I tell you how pretty you are? You’re gorgeous… so pliant and wonderful. I’m sure you’d be even prettier with— with Nightmare’s fingers stretching you open. What do you think, do you want that?”

“Please!” Dust cries out, squeezing his sockets shut as he shakes in Horror’s hold, clenching his teeth.

“You heard the man, Nightmare.”

“Oh, I’ve heard him alright,” Nightmare mumbles, licking his teeth moving Dust’s left leg to rest over his shoulder. “Alright, Dust?”

He pauses, looking up and propping himself with one arm. Dust looks down, cocking his head in inquiry and blinking the moisture out of his eyes.

“You want me to stop, you tell me,” Nightmare tells him, leaving no room for rebuttal, which, of course, means Dust gives a rebuttal.

“I can’t feel much pain,” he reminds them, chest heaving heavily. 

“All the more reason to stop us as soon as you feel any.” Dust just blinks, making Nightmare frown. “You know, I won’t continue if you don’t agree.”

“Okay, okay, I’ll tell you,” spills from Dust’s mouth immediately, “Just, please…”

The corners of Nightmare’s teeth twitch up almost simultaneously. “Good boy,” he praises and Dust’s breath hitches.

Nightmare’s fingers make their way between Dust’s legs, circling his entrance and rubbing through the folds. Dust jerks, toes curling as the first finger pushes inside, just past the first knuckle and then back out only to repeat it, trying to get him to relax.

“Kiss me,” Horror demands, reaching up to grasp Dust’s chin and turn his head so he can clink their teeth together.

Horror’s tongue is skilled, swarming Dust’s mouth and running over each nook and cranny and tangling with his. Dust gets lost in the messy kiss easily, gasping for air he doesn’t need whenever Horror lets him. Nightmare works his fingers in; Dust doesn’t even notice when a second one starts prodding at him until it’s all the way in and Nightmare curls them.

Dust arches his back as his eyesockets slip closed. Horror nuzzles into his neck, licking the spaces between his vertebrae, where magic pools and sparks, and Dust can only crane his head to the side to give him more space.

Nightmare keeps moving, his fingers curling and running over the soft walls, stretching them until they’re pliant and _wet_ and practically opening up for his fingers. He has no problems adding a third one then.

“More… more more more,” Dust mutters, panting with an open mouth, with a line of spittle running down his chin. “Please, Nightmare…”

Horror chuckles quietly behind him, running a hand down from Dust’s chest, the drag of his claws going from rough bones onto soft ecto a sensation that makes Dust shiver, to curl around his cock. More purple-tinted precum oozes out of the tip and he swipes it with a thumb, spreading it along the flesh as he starts pumping it, falling into rhythm with Nightmare almost effortlessly.

Dust is putty between the two of them, hips bucking up into Horror’s fist, only to fall back down and impale himself further on Nightmare’s fingers. And then Horror starts thumbing at the tip again, a phalange rubbing across the leaking slit and it has Dust going wild, one hand gripping Nightmare’s tentacle and the other up by his shoulder, fingers entwined with Horror’s and squeezing so tight it should hurt. But he doesn’t have the mind to think about that and Horror doesn’t complain.

“Please, please,” he keeps repeating, words slowly slurring together as his head hangs back against Horror’s shoulder.

“You sound so lovely. All these pleas and noises... you have no idea how... turned on I am right now. Nightmare, too… Look. He’s fucking his own hand to your voice. You want more, lambchop? Would... you like me to fuck you?” Horror asks quietly, voice barely above Dust’s pants.

“Yes!” Dust cries, Horror’s voice doing wonders to his insides. “Please, stars, I want you, please.”

Nightmare pulls out his fingers with a wet squelch, groaning softly as he sits back up, still pumping himself. He lets go, bucking up once or twice into thin air, in favor of grasping Dust’s hips and lifting him up to help position him.

“You’re so light,” Nightmare comments, holding Dust with a single tentacle wound around his ecto-stomach.

Horror sits properly, propping the pillows so he can lean back. He holds up his dick, sockets fluttering at the much needed contact and he locks eyes with Nightmare, grinning lazily as his shoulders rise and drop with his labored breathing.

“Take it slow,” he says. Dust isn’t sure whether it’s addressed to him or Nightmare, but it doesn’t matter much when Nightmare lowers him onto Horror’s cock with a kiss, gravity and bucking knees pulling him down onto it.

His mouth opens in a wordless scream, hands flying out and wrapping around Nightmare’s shoulders, nails digging into his back and leaving behind half crescents on the dark goop. Horror is pressing kisses along the back of his neck, mumbling nothings to shush him, trying his best to make it easier on him.

Except Dust’s body hums with pleasure, back taunt as a bow as he sinks as far as he can on Horror’s cock, insides opening up for it.

“You okay?” Nightmare asks, brushing his sweat off of his face. Dust unconsciously leans into the touch, nuzzling his face against the palm.

He nods vigorously, though he doesn’t open his sockets again just yet. He isn’t even sure when he’d closed them.

“Horror, please—!” Dust begs, twisting between them and surging forward to be able to kiss Nightmare, meshing their mouths together in a messy tangle of tongue and teeth.

Horror gets the message, though, and replaces Nightmare’s hands on Dust’s hips, pulling him up so he can let him fall back down. Both of them groan, Dust’s sounds muffled by Nightmare’s mouth. Dust holds onto Nightmare even tighter, if it’s even possible, body shuddering badly with every bounce. Horror’s snap up as much as they can given the position, and his cock rubs at Dust’s insides in all the right ways.

“You’re so pretty,” Nightmare mutters, forehead brushing Dust’s.

He slots himself between his legs again, chest to chest; Dust shudders as the goo drips down onto him, splotches of black hitting his sensitive ribs and rolling down his ecto-flesh.

“All those pretty sounds… You can be loud if you want, you know?” Nightmare keeps talking, down into Dust’s ear as he pecks Horror’s teeth over his shoulder.

“Yeah… We’d love to hear more,” Horror agrees, doing his best to maintain a steady pace. A mixture of his and Horror’s fluids drips from Dust, falling to the sheets and painting them with red and purple. Dust’s lilac precum spreads all over Nightmare’s lower abdomen when he ruts against the other, cocks sliding together wetly and so, so well.

As if on that cue, Dust lets out a long whine, rubbing back and ruining Horror’s pace with his uncontrollable hips. Nightmare latches onto the other side of his neck, leaving his own bites opposite Horror’s, and then moves up to kiss Dust again, to swallow those moans at the roots.

Dust breaks away with a plea on his tongue, something completely incomprehensible, too slurred and quiet to make out, but it’s written all over his pale, lilac-flushed face, his eyelights misted and shaped vaguely like hearts and tears flooding from the corners of his sockets.

“We got you,” Nightmare mutters, grinding his hips into the other’s. Horror looks just as flushed, but Nightmare is sure he himself looks the same. The air around them is buzzing with their magic, like a spark ready to ignite at any moment.

“I—” Dust whimpers, nails raking across Nightmare’s shoulder blades and digging through the goop until they touch bone. Nightmare hisses and sinks his teeth into Dust’s shoulder as payback, only for Dust to moan louder. He’s not able to get a coherent thought out, it seems. “I’m— You’re— Fuck—”

Horror releases his vice-grip on Dust’s hips to worm his hand between him and Nightmare, wrapping his hand around both of their cocks.

Dust wails, voice starting to echo in the bedroom. Nightmare almost slumps forward, catching himself with both arms around the two’s heads, braced against the wall as he hangs his head onto Dust’s shoulder.

“You know… just how to do it,” he tells Horror, who can only grin weakly, tightening his hold and bucking up. Dust bounces in his lap, fucking his fist and making Nightmare close his eye as liquid pleasure strikes through his veins like electricity.

“You… two are too precious to pass up,” Horror mutters back, feeling a coil in his stomach. He’s about to warn the others he’s close when Dust seizes up between them, arching his back so much that Horror’s cock almost slips out of him.

Dust’s throaty moan echoes throughout the room for long seconds in which purple cum splashes Nightmare’s stomach.

Horror whines, digging his claws into Dust’s hip as his toes curl and he rides out his own orgasm, the world blacking out around him for a minute or two. Nightmare is the last one, after a few more uncoordinated thrusts, staring at his lovers’ blissful, fucked-out faces with a wide-blown eye.

However, Nightmare is the first one to come back to himself, collapsing backwards onto the soft covers. Dust follows after him, bonelessly slumping against Horror’s bigger chest. Both of them slowly regain their breath and their consciousness, and Horror flutters his eyes open to look at Nightmare.

“I… definitely think Dust should— should join us again,” Horror says, leaving a butterfly kiss on Dust’s shoulder, right over a bright shape of his own teeth that not even his shirt will hide. “You’ve no idea how good it feels… inside you,” he whispers, moving his kisses along the side of Dust’s skull.

Dust shudders, his softening cock giving a last pathetic jerk and a heavy glob of cum that rolls down its length.

“Let’s get you off before Horror gets hard again,” Nightmare laughs, shuffling closer to gently scoop Dust’s form up in his tentacles.

Horror feigns being upset, but he leans forward and kisses Nightmare nonetheless. His ecto is long gone, but just the thought that one day, Horror would have enough magic to last another round is tantalizing. “How are you feeling?”

“Great. You, Dust?” Nightmare replies without a hesitation. Good, he knew it was a question for the both of them.

“That was… I don’t have words,” Dust says truthfully, body feeling boneless as he blinks the remnants of dark edges from his vision. 

“Thumbs… up or down?” Horror asks.

Dust doesn’t take so long to answer this time. “Thumbs up.”

Horror’s face lights up like a hundred watt light bulb. “Y’hear that, Night? We got a thumbs up… for our first time!”

Dust turns around in Nightmare’s lax hold to press a kiss to Horror’s cheek. And then he promptly passes out, the glow of his ecto-body fading as it dissolves.

Nightmare laughs mirthfully. “I don’t think you can get any better.”

Horror shuffles onto his knees while Nightmare sets Dust down to lay, and captures Nightmare’s teeth as soon as he makes sure Dust is comfortable. “Prob’ly not,” he mutters into the kiss.


End file.
